The passing and overtaking of vehicles which are driving slowly, especially on two-lane roads, creates safety hazards due to sudden, emerging, oncoming traffic. When passing is desired, and the slower vehicle ahead is large or wide, as for example trucks and buses, it is difficult for the faster, following vehicle to be aware of oncoming traffic which would prevent passing. In order to allow safe passing by overtaking vehicles, the passing vehicle must pull out far to the left before beginning to pass so that the driver can decide whether or not it is safe to pass. Providing improved vision around large vehicles such as trucks or buses without requiring dangerous movement into the opposite lane to determine whether passing can take place is a highly desirable result for improved safety.
One attempted solution to this problem is shown in German Offenlegungschrift DE 29 18 822 which discloses an exterior rearview mirror for vehicles by which the oncoming traffic is made visible for the driver by a deviation mirror. The arrangement of a number of mirrors within an exterior rearview housing results in a bulky mirror housing which as a part projecting laterally from the vehicle creates a risk of damage in parking lots or similar narrow lanes.
Another attempted solution is shown in German Offenlegungschrift DE 23 52708 which discloses an optical system for vehicles which includes an arrangement of prisms for displaying oncoming traffic. However, the field of view for the driver offered by the prisms is too small for his determining safely the traffic situation ahead of the vehicle.